(b) A transistor with a height of 0.4 cm and a diameter of 0.6 cm is mounted on a circuit board as shown in Figure 3. The transistor is cooled by air flowing over it with an average heat transfer coefficient of 30 W/m².K. If the air temperature is 55°C and the transistor case temperature is not to exceed 70°C, determine the amount of power this transistor can dissipate safely. Disregard any heat transfer from the transistor base. Air 55°C ↓↓↓↓ Power transistor 0.6 cm T₂ ≤ 70°C -0.4 cm- Figure 3

(b) A transistor with a height of 0.4 cm and a diameter of 0.6 cm is mounted on a circuit board as shown in Figure 3. The transistor is cooled by air flowing over it with an average heat transfer coefficient of 30 W/m².K. If the air temperature is 55°C and the transistor case temperature is not to exceed 70°C, determine the amount of power this transistor can dissipate safely. Disregard any heat transfer from the transistor base. Air 55°C ↓↓↓↓ Power transistor 0.6 cm T₂ ≤ 70°C -0.4 cm- Figure 3

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.19P: 1.19 A cryogenic fluid is stored in a 0.3-m-diameter spherical container is still air. If the...

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1.19 A cryogenic fluid is stored in a 0.3-m-diameter spherical container is still air. If the convection heat transfer coefficient between the outer surface of the container and the air is 6.8 , the temperature of the air is 27°C, and the temperature of the surface of the sphere is –183°C, determine the rate of heat transfer by convection.
2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from one side of an electronic device 1 m wide and 1 m tall. The fins are to be rectangular in cross section, 2.5 cm long and 0.25 cm thick, as shown in the figure. There are to be 100 fins per meter. The convection heat transfer coefficient, both for the wall and the fins, is estimated to be K. With this information determine the percent increase in the rate of heat transfer of the finned wall compared to the bare wall.
1.29 A spherical interplanetary probe with a 30-cm diameter contains electronic equipment that dissipates 100 W. If the probe surface has an emissivity of 0.8, what is its surface temperature in outer space? State your assumptions in the calculations.
A pipe carrying superheated steam in a basement at 10C has a surface temperature of 150C. Heat loss from the pipe occurs by radiation (=0.6) and natural convection (hc=25W/m2K). Determine the percentage of the total heat loss by these two mechanisms.
Heat is lost through the glass pane of a window. The thickness of the glass is 3 mm, and the window is 0.9 m by 1.8 m. The thermal conductivity of glass is 0.8 W/mK. If the temperature difference across the glass is 17 K, what is the total heat transfer through the pane of glass? Give your answer in Watts to the nearest integer.
It is designed in such a way that the internal temperature of a commercial heat treatment furnace can reach up to 165 oC. All surfaces of the furnace consist of firebrick (10 cm), insulation material and sheet metal (3mm) from the inside out. Given that the outdoor temperature is 22 oC, the outer sheet will be allowed to go up to 35 oC, which is a temperature that will not disturb in contact with hands. In this case, determine the insulation material thickness to be used. The thermal conductivity coefficient of the insulation material is insulation 0.066 W / m oC, 60 W / m oC for sheet metal and 115 W / m oC for firebrick. Indoor heat transfer coefficient will be accepted as 25 W / m2 oC and 12 W / m2 oC for outdoor environment.
A wall with a thermal conductivity of 0.4 W/m-°C is maintained at 45°C. The heat transfer through the wall is 220 W. The wall surface area is 2.0m² and its thickness is 1.5 cm. Determine the temperature at the other surface.
A 4-mm and 2-m-long electric wire is tightly wrapped with a 2-mm-thick plastic cover whose thermal conductivity is k =0.1 W/m-°C. Electrical measurements indicate that a current of 10 A passes through the wire and there is a voltage drop of 10 V along the wire. If the insulated wire is exposed to a medium at =20 °C with a heat transfer coefficient of h=10 T. W/m2.°C, determine the temperatures T1 and T2 as shown in the figure below. Also determine whether doubling the .thickness of the plastic cover will increase or decrease T2 T
It is designed in such a way that the internal temperature of a commercial heat treatment furnace can reach up to 165 oC. All surfaces of the furnace consist of firebrick (10 cm), insulation material and sheet metal (3mm) from the inside out. Given that the outdoor temperature is 22 oC, the outer sheet will be allowed to go up to 35 oC, which is a temperature that will not be disturbed by hand contact. In this case, determine the insulation material thickness to be used. Insulation material thermal conductivity coefficient is 0.066 insulation W / m oC, 60 W / m oC for sheet metal and 115 W / m oC for firebrick. Indoor heat transfer coefficient will be accepted as 25 W / m2 oC and 12 W / m2 oC for outdoor environment.
An oil radiator has an outside surface area of 0.18 m2 and operates at a surface temperature of 85 degree Celsius. If air moves over the surface of the radiator at a temperature of 16 degree Celsius and gives rise to a heat transfer coefficient equal to 38.25 W/(m2-K). Find out the heat transfer flux? O 2923 W/m2 O 3801 W/m² O 2639 W/m² O 1659 W/m²
The inner and outer surfaces of a cylindrical shell with radii of 1 cm and 2 cm are 300 °C and 100 °C, respectively. If the thermal conductivity of the shell is 2 W/m-K, determine the heat transfer through the shell per unit length of the cylinder.
A pipe 30 m long with an outer diameter of 75 mm is used to deliver steam at a rate of 1500 kg / hour. The vapor pressure is 198.53 kPa entering the pipe with a quality of 98%. The pipe needs to be insulated with a thermal conductivity of 0.2 W / (m K) so that the quality of the steam will only slightly decrease to 95%. The outer surface temperature of the insulation is assumed to be 25 ° C. Ignore resistance conductive of the pipe material and it is assumed that there is no pressure drop in the pipe. a. Determine the enthalpy of incoming vapor = Answer kJ / kg. b. Determine the enthalpy of steam coming out = Answer kJ / kg. c. Determine the vapor heat change / loss along the flow = Answer watt. d. Specify the minimum required insulation thickness = Answer cm.